The present embodiments relate generally to harvesting environmental energy. More particularly, the present embodiments relate to harvesting energy from radio frequency (RF) signals to power a sensor node and/or wireless radio.
Wireless sensor networks (WSNs) of so-called “smart” sensors can be used in remote monitoring and control applications. However, in almost all applications that involve WSNs, there is a trade off between the need to sense and communicate useful information and the requirement to do so in an energy efficient manner. A WSN, once deployed, may be intended to work for long periods of time with only minimal human intervention. For instance, remote monitoring applications may include individual sensor nodes, numbering into the hundreds or even thousands, that each run on a limited supply of energy, such as a battery. As a result, with conventional sensor nodes, excessive on-board processing and, perhaps more importantly, frequent invocation of the sensor node's radio may rapidly deplete the on-board energy source. Therefore, there is a need to develop sensor network protocols and algorithms with energy-efficient and self-organizing capabilities.
Additionally, replacing depleted batteries may be inefficient or impractical. A network may include a large number of individual sensor nodes that may be difficult to access due to being implanted within a wall, a ceiling, a larger device, or a patient. Accordingly, there is also a need for novel energy harvesting schemes operable to power wireless sensor nodes, as well as automatically replenish on-board energy storage units.